Wireless communication systems have developed through various generations, including a first-generation analog wireless phone service (1G), a second-generation (2G) digital wireless phone service, including interim 2.5G and 2.75G networks, and a third-generation (3G) high speed data Internet-capable wireless service. There are presently many different types of wireless communication systems in use, including Cellular and Personal Communications Service (PCS) systems. Examples of known cellular systems include the cellular Analog Advanced Mobile Phone System (AMPS), and digital cellular systems based on Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), the Global System for Mobile access (GSM) variation of TDMA, and newer hybrid digital communication systems using both TDMA and CDMA technologies.
The method for providing CDMA mobile communications was standardized in the United States by the Telecommunications Industry Association/Electronic Industries Association in TIA/EIA/IS-95-A entitled “Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System,” referred to herein as IS-95. Combined AMPS & CDMA systems are described in TIA/EIA Standard IS-98. Other communications systems are described in the IMT-2000/UM, or International Mobile Telecommunications System 2000/Universal Mobile Telecommunications System, standards covering what are referred to as wideband CDMA (WCDMA), CDMA2000 such as CDMA2000 1xEV-DO standards, for example, or TD-SCDMA.
In wireless communication systems, mobile stations, handsets, or access terminals (AT) receive signals from fixed position base stations, which can also be referred to as cell sites or simply cells that support communication links or service within particular geographic regions adjacent to or surrounding the base stations. Base stations provide entry points to an access network (AN) such as a radio access network (RAN), which is generally a packet data network using standard Internet Engineering Task Force (IETF) based protocols that support methods for differentiating traffic based on Quality of Service (QoS) requirements. Therefore, the base stations generally interact with ATs through an over the air interface and with the AN through Internet Protocol (IP) network data packets.
In wireless telecommunication systems, Push-to-talk (PTT) capabilities are becoming popular with service sectors and consumers. PTT can support a “dispatch” voice service that operates over standard commercial wireless infrastructures, such as CDMA, FDMA, TDMA, GSM, etc. In a dispatch model, communication between endpoints, which can be, for example, ATs, occurs within virtual groups, where the voice of one “talker” is transmitted to one or more “listeners.” A single instance of this type of communication is commonly referred to as a dispatch call, or simply a PTT call. A PTT call is an instantiation of a group, which defines the characteristics of a call. A group in essence is defined by a member list and associated information, such as group name or group identification.
Conventionally, data packets within a wireless communication network have been configured to be sent to a single destination or access terminal. A transmission of data to a single destination is referred to as “unicast”. As mobile communications have increased, the ability to transmit given data concurrently to multiple access terminals has become increasingly important. Accordingly, protocols have been adopted to support concurrent data transmissions of the same packet or message to multiple destinations or target access terminals. A “broadcast” refers to a transmission of data packets to all destinations or access terminals such as within a given cell, served by a given service provider, and the like, while a “multicast” refers to a transmission of data packets to a given group of destinations or access terminals. In an example, the given group of destinations or “multicast group” may include more than one and less than all of possible destinations or access terminals within a given group, served by a given service provider and the like. However, it is at least possible in certain situations that the multicast group comprises only one access terminal, similar to a unicast, or alternatively that the multicast group comprises all access terminals within a given cell similar to a broadcast.
In addition to various transmission schemes that may be used such as unicast, multicast, broadcast as described herein, a PTT call may also be a half duplex or a full duplex communication for at least some of the participants. Generally, a PTT call corresponds to a server mediated communication between two or more identified access terminals, regardless of the various configurations used to conduct the PTT calls. A dispatch console can often serve as the mediating server or entity for multiple calls including PTT calls. Difficulties can arise in circumstances where a dispatch console enters a faulty state such as a software crash, reboot, power failure or the like. In such circumstances, the dispatch console can lose information about the state of the PTT call including call states and the like. When a dispatch console restarts after a failure the reset user interface of the dispatch console is inconsistent with the actual state of the call including call clients that were added or dropped while the dispatch console was down, and synchronization of any content, such as multimedia content that was being streamed during the outage. While protocols exist for call set up, there is a need to manage the restoration of calls when an entity such as a dispatch console fails and is either restarted or the session resumed on a new console.